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Electronic cigarettes are lawful and their nicotine liquid can legally be imported via the internet for personal use. But it is illegal to sell the so-called "e-juice" - which produces a nicotine vapour when heated in the battery-powered devices - until the product is approved as a quit-smoking medicine.

The Ministry of Health does not support e-cigarettes and official medical guidelines on how to quit smoking do not mention them.

"The ministry's position is really disappointing as it produces barriers to accessing nicotine liquid," says Dr Winiata.

He suggests e-cigarettes to smokers who either refuse to stop or have tried repeatedly to quit by using Champix and other medications.

Dr Winiata was influenced by Public Health England, which estimates e-cigarettes are around 95 per cent less harmful than smoking, and by Britain's College of Physicians, which concluded vaping should be widely promoted as a substitute for smoking.

A New Zealand survey found nearly 1 per cent of all adults and 4 per cent of adult smokers were using e-cigarettes.

The ministry stands by its precautionary approach, necessary because of a lack of evidence to support e-cigarettes as a quit-smoking aid, the potential harm of long-term use, and the variable contents and quality of the products, it says.

New Zealand is not expected to reach the Government's Smokefree 2025 target of less than 5 per cent smoking on the strength of tax increases alone. The Treasury's estimate is that the Budget's continuation until 2020 of the 10 per cent annual increases in tobacco excise - which began in 2010 - will only bring the rate down to 12 per cent by 2025.

Public health experts offer a range of solutions to reach 5 per cent. Many suggest much bigger tax increases, but there is growing opposition to hitting smokers' pockets ever harder.

Dr Winiata says a number of his Mangere clinic's patients have quit smoking by vaping, but he points to the greater impact of e-cigarettes across town.

Of 30 people to go though the Vape2Save programme, 24 - 80 per cent - have quit smoking since it began in November. Rebecca Ruwhiu-Collins of Te Waipuna Puawai, part of the Sisters of Mercy, says she began the courses because of the tax increases' effects.

"The community in Glen Innes, Panmure, Point England, they are struggling as it is now with their tobacco addiction. The taxes were really hurting these families."

She cited a large family in which the parents spent $200 a week on tobacco. The mother has switched to vaping and the father is doing the course now and together they spend $15 a week on liquid nicotine. This "massive reduction" in costs had changed their lives.

She urges the Government to allow sales of liquid nicotine to adults at pharmacies or other regulated vendors, because many aren't able to manage internet imports. Course participants have taught each other how, using library computers and prezzy cards.

Tobacco control expert Dr Marewa Glover, of Massey University, said New Zealand urgently needed to permit nicotine sales as a consumer product to help the "hardened" smokers now being marginalised by tax increases expected to push a packet of 20 smokes to $30 in 2020.

She points to ministry survey data showing no statistically significant drop in Maori smoking prevalence since the tax rises began in 2010.

However Otago University Wellington tobacco researchers, who are more wary of e-cigarettes, say the 2013 Census did show a drop since 2006, from 42.2 to 32.7 per cent.

Christchurch tobacco researcher Dr Murray Laugesen calculates that with annual tax increases of 15 per cent plus full legalisation of e-cigarettes, smoking prevalence could fall to 3 per cent in 2025.

The Otago University researchers fear e-cigarettes could become a gateway back to smoking becoming a normal behaviour again. Dr Tony Blakely says it is unclear whether they would reduce smoking prevalence because smokers might use tobacco and an e-cigarette.